A number of semiconductor lasers, laser array, optical amplifiers, and optical amplifier arrays have been recently developed for high power application. These, in addition to diode lasers used in communications, benefit greatly if used in conjunction with isolators capable of preventing reflections from reentering the laser or amplifier. In addition, a number of integrated optic devices, such as switches and modulators, which are useful in optical communications would benefit if there were available isolators that could be integrated directly on the same substrate as the device.
Briefly, isolators protect the lasers from instabilities resulting from external reflection. They can be used to avoid the problem of multi-mode operation in linear GSE arrays by allowing only unidirectional flow of light to lock up the array members. Further, the use of an isolator can help stabilize the operation of semiconductor master-oscillator power amplifier devices. In addition to these, there are many other areas in optical communications, fiber optic telephony and integrated optics which are improved by the use of optical isolators to separate various system components.
To date there have been no isolators that can be monolithically integrated with semiconductor sources and/or amplifiers or with many electro-optic or passive waveguide devices. Waveguide optic isolators, to date, have been based on Faraday rotation types in crystalline magnetic garnet waveguides that generally cannot be grown or deposited on other material systems. Therefore, it would be desirable to have an isolator material which can be deposited on other material systems, particularly the semiconductor materials used to form semiconductor lasers and other optical devices, to be able to form an isolator integrated with the optical devices containing a waveguide.